It is well known that any significant reduction or restriction in the flow of blood through the arteries of the body can cause complications which may have serious consequences. As a result, it is extremely important for the health of the patient that a stenosis, or blockage, which is causing such a condition be eliminated. One well known and frequently used procedure to accomplish this task is popularly known as angioplasty. For a basic angioplasty procedure, a dilatation balloon is positioned in the arterial lumen at the stenosis and the balloon is inflated to open the artery by dilating the plaque-restricted lumen at the stenosis. With angioplasty procedures, however, the plaque, remains in the artery and is not removed. Unfortunately, in some cases, it appears that the plaque which is left behind in the artery may cause a re-stenosis in the artery.
As an alternative to angioplasty, atherectomy procedures have been developed to resolve the problems caused by blocked arteries. However, unlike an angioplasty procedure, the atherectomy procedure mechanically cuts and then removes the plaque which is creating the stenosis from the artery. The cutting devices which are used for this task must, of necessity, be rather small. They must also have sufficient structural strength to cut the plaque in performance of the atherectomy procedure. Additionally, they must be operationally reliable. Many examples of such cutting devices can be given. For instance, U.S. Pat. No. 4,895,166 which issued to Farr et al. for an invention entitled "Rotatable Cutter for the Lumen of a Blood Vessel" and which is assigned to the same assignee as the present invention, discloses a cone-shaped cutter which may be rotatably advanced through a vessel to remove stenotic material. Alternatively, U.S. Pat. No. 4,589,412 which issued to Kensey for an invention entitled "Method and Apparatus for Surgically Removing Remote Deposits" discloses a triangular rotatable cutter which cuts stenotic material as it is rotatably advanced through a vessel.
One problem which must be confronted in any procedure, whether it be an angioplasty or an atherectomy procedure, is the size of the entry site which can be used for introducing the medical device being used into the artery. Standard practices accept an entry site which has a diameter of only approximately twelve French, or approximately four millimeters. Thus, any device which is to be positioned in the artery must pass through a guide catheter whose outer diameter is not larger than twelve French. The inner diameter of such an introducer is generally, however, on the order of only nine French. The consequence is that any device which is effectively insertable into the artery of a patient must be capable of assuming a configuration wherein the greatest dimension across the device is no more than approximately nine French. It happens, however, that to properly clear a stenotic segment it is sometimes necessary to create a lumen through the stenotic segment which has a greater diameter than nine French. To do this by an atherectomy procedure, the cutter being used must be capable of expanding beyond the nine French restriction imposed at the entry site.
Several examples of expandable cutting devices which are specifically useful as medical devices for atherectomy procedures can be given. For instance, U.S. Pat. No. 4,966,604 which issued to Reiss for an invention entitled "Expandable Atherectomy Cutter with Flexibly Bowed Blades" and is assigned to the same assignee as the present invention, discloses a rotatable atherectomy cutter whose flexible blades may be bowed outward to give the cutter a variable cutting radius. Alternatively, U.S. Pat. No. 4,986,807 which issued to Farr for an invention entitled "Atherectomy Cutter with Radially Projecting Blade" and is also assigned to the same assignee as the present invention, discloses a rotatable cutter featuring a single blade which may be selectively extended thereby increasing the cutting radius of the cutter. There is, of course, still a need for other expandable atherectomy cutters which can meet the specific needs of a specifically desired protocol.
Another problem which must be confronted in an atherectomy procedure is the existence of loose plaque which is necessarily generated as the stenotic segment is cut. It may be appreciated that failure to remove plaque of this type may adversely effect the health of the patient involved. In some cases, these adverse effects may be severe. As a result, atherectomy devices generally employ some means whereby loose plaque may be removed from the patient as the stenosis is cut. To this end, many atherectomy devices include means that allows fluid to be forcefully removed from the cutting site. As the fluid is removed, plaque fragments cut from the stenotic segment are carried with the fluid and removed from the patient. Practice has shown that removal of fluid from the cutting site is generally an effective technique for reducing the quantity of loose plaque within a vessel undergoing an atherectomy procedure. It is still the case, however, that loose stenotic material may remain in the vessel after completion of the atherectomy procedure. This is particularly true in cases where advancement of the atherectomy device within the vessel causes the cutter to move past cut plaque before it is removed from the vessel. As a result, it is clear that improved methods for removing loose plaque are generally desirable.
Another problem which must be confronted in an atherectomy procedure involves the wide variation in locations in which stenotic segments may occur. Specifically, it happens that atherectomy procedures can be performed in the coronary arteries, the carotid arteries, the renal arteries, and in the peripheral arteries. Each set of arteries is different and presents different challenges to the atherectomy procedure. As a result, there is the need to provide a generalized technology for atherectomy devices which may be easily adapted to the needs of varying atherectomy procedures in varying locations.
In light of the above, it is an object of the present invention to provide a compressible/expandable atherectomy cutter which features a small diameter compressed configuration and a large diameter expanded configuration. Still another object of the present invention is to provide a compressible/expandable atherectomy cutter which includes an enhanced ability to remove loose stenotic material from the cutting site. Yet another object of the present invention is to provide a compressible/expandable atherectomy cutter which reduces the probability that loose stenotic material will pass the advancing cutter before such material may be removed. Still another object of the present invention is to provide a compressible/expandable atherectomy cutter which whose basic design may be easily adapted to suit the needs of different atherectomy procedures. Yet another object of the present invention is to provide a compressible/expandable atherectomy cutter which is relatively simple to use, relatively easy to manufacture, and comparatively cost effective.